High-frequency apparatus



Aug. 22, 1944.

HIGH FREQUENCY APPARATUS Filed Dec. 30, 1941 c. D. KENTNER z INVENTOR-642w KEA/IX/E'e ATTORNEY Patented Aug. 22, 1944 UNITED STATES PATENTOFFICE M Qzssazso I "HIGH-FREQUENCY APPARATUS Carroll DaleKentner,Medfordfliakesyli. .1., assigner toRadio Corporation of America, acorporation ofDelaware H v a v 30, l94-l,-SerialNo. 424,992 3Claimsi(o1. ass-27.5)

' I Application December My invention relates .to "electron dischargedevices, particularly to transmitter tubes for high frequency operation.

The object of my invention is to provide an iniproved radio tubemounting and shielding arrangement particularly useful for screen gridtubes.

Another object of my invention is to provide a new and useful radiofrequency by-pass condenser for election discharge devices. A feature ofthis invention is the novel circumferential arrangement of a capacitivecoupling between an electrode of an electron discharge device andground, thus providing a short radio frequency path to ground. Thisfeature is of great importance in a radio frequency modulationtransmitter because of the very high frequencies encountered. I

This invention is shown, but notclai-med, in a patentapplication ofArthur K. Wing, Jr., filed January 2, 1941, Serial #372,867 which hasnow matured into United States Patent 452,288,380, issued June 30, 1942.

The characteristic features of my invention are defined in the appendedclaims and the preferred embodiment thereof is described in the f 01-lowing specification and shown in the accompanying drawing in whichFigure 1 is a longitudinal half-section of a'tube and shieldingarrangement, and Figure 2 is a plan view of Figure 1-.

The anode l is of the externally cooled type and encloses co-axialscreen grid 2, control grid 3 and cathode 4. The two grids arecylindrical, each comprising a plurality of parallel grid wires arrangedin-a-circle and held at their ends by collars. The cathode showncomprises a single helix of electron emissive metal such as tungsten orthoriated tungsten supported at its upper end on the central rod 5,the'rod being joined at itslow'er end'to the bridge structure 6 which inturn is clamped at its opposite ends to the two lead-in conductors I forthe cathode. The control grid lead-in conductors, not visible in Figure1, are of the same size and shape as the cathode lead-ins and in a planenormal to the plane of the cathode lead-ins. The four bushings 8 for thelead-in conductors comprise, preferably, glass cylinders eachhermetically joined at one end to a metal disc and at the other end to ametal sleeve, which is in turn brazed to openings in the sheet metalheader 9.

The rim portion of the header is rolled or pressed with a channel I l,substantially U-shaped in cross section, and the glass bulb I is joinedtoth'e outercylinder of the channel. Flexibility of the outer cylinderin a radial direction minimizes strains in the glass o f-the bulb attheseal and thermally isolates "this seal region from the glass-to-metalseals of the bushings 8.

The header, according to my invention, comprises the sole support forthe grid and cathode electrodes, [and although the header is made ofthin sheet metal it will rigidly hold the electrodes in their positionin the tube "and will withstand warping caused by heat and atmosphericpressure, which pressure may be upward of 140 pounds on a header only3.5 inches in diameter. I propose; according to my invention, to concavethe header inwardly as shown. The reentrant concavity of the header notonly strengthens the header but provides a convenient protecting recessfor thelead-in bushings '8. One convenient way to make my novel headeris to spin or press the sheet'material with asubstantially hemisphericalor conicalportion I2 and with the channel ll along the rim of thehemisphere. Die punches may then be used to flatten seats for thebushings Bin the bottom portion of the header. The exhaust tube I3 isjoined to the center of -the bottom. of theheade'r, the sheet metalaround the exhaust tubebe'irig further stiffened by an embossed annular'groove around the exhaust tube junction. My header is easily made fromrelatively lightweight sheet metal and without the usual heavyreinforcing metal plate across the end of the tube. The electrodes maybe supported directly on the header with no bracing means orelectrode-to-envelope spacers and with negligible displacement of theelectrodes during manufacture and use.

The screen grid is supported at the small end of the metal cone M which,at its larger end,

-. is slipped over the rim portion of the header and into the channel Il andspot welded. The screen grid cone is coaxial with the electrodes;and is electrically connected to the metal header 9, and completelyencloses the lead-in conductors for the cathode and control grid andshields these conductors from the anode.

The cathode support rod 5 is inserted at its lower end in an eyelet l5which is held against the upper side of the insulating bar l6 of thebridge structure 6 and is drawn in snug contact with the bar by metalstrap l'l drawn tightly over the head of the eyelet by the bolt 18 witha tapered head and tapered washer. As the bolt is tightened the strap isdrawn downwardly and into the tapered hole in the ceramic. Opposite endsof the bar It are bolted to clamps engaging the cathode lead-inconductors I just inside the header. The heating circuit for the cathodeis completed from one conductor through the heat shield l9, through thesupport rod 5, through the heating coil 4 and thence through the otherconductor 1 insulatingly joined to the heat shield by the ceramicbushing 20. The heat shield 19, being larger in diameter than the smallend of the cone, cooperates with the cone to prevent heating by thecathode, of the bridge structure 6 and of the glass-to-metal seals ofthe lead-in bushings 8.

The anode may be cooled according to my invention with an air radiatorcomprising fins 2| integrally joined to a hub 22 which in turn may beshrink-fitted by differential expansion on a' sleeve 23. The sleeve 23is then soldered to the been obtained in making transmitter tubes of thetype commercially known as the 827R, where the high frequency outputpower is one kilowatt at 108 megacycles or 1.5 kilowatts at 50megacycles. The diameter of the anode is about 1.5 inches, the anodelength 2.25 inches, the header outside diameter 3.6 inches, the overalllength of the tube 4.5 inches, and the header of commercial .030 inchnickel-iron-cobalt alloy sheet. The filament carries 25 amperes andoperates at about 2000 K. The upper part of cone I4, the grid wires 1and metal parts adjacent the filament are preferouter surface of theanode to provide a low re- I sistance heat conducting band between theanode and the fins. The radiator fins and hub may be formed by extrusionfrom aluminum or other good heat conducting material and the sleeve andanode wall made, preferably, of copper, which is joined to fins 22 bymeans of a shrink fit.

The washer-like disc or collar 24 at the upper end of the control grid 3is provided with a series of holes circularly arranged to receive theends of the control grid wires. To obviate buckling or bowing of thesewires because of unequal heat expansion, the wires are p'assedfreelythrough the holes in the washer, the washer being held in place by tabswelded to only two or three of the grid wires. A metal or ceramic washerwas found unsuitable because of difficulty in obtaining free movement ofthe wires through the holes in the washer without either binding orexcessive looseness. It has been found that a graphite or carbon washerideally meets the requirements of the spacing collar. Graphite issufiiciently refractory to withstand the high temperatures and will notbind the grid wires when hot.

To form a radio frequency screen grid by-pass condenser the entire tubeassembly may conveniently be supported upon a metallic electrode plate25 with a large central opening to clear the lead-in bushings 8.Electrical connection to the header and to its attached screen grid ismade by a number of flexible spring fingers 26 fastened as by spotwelding to the upper surface of the plate 25 and arranged around theperiphery of the header. The header 9 and its connected screen grid 2 isthus grounded for radio frequency potentials by capacitively couplingthe screen grid to ground through an annular dielectric sheet to aground plate. The curved surface greatly reduces the tendency to causecorona brushing. A thin, flat, ring-shaped insulator 28 of micaapproximately coextensive with the rim of the header, separates theelectrode plate 25 from the other electrode or metal plate 21 of thegrounded transmitter chassis.

Good results, according to my invention, have ably of tantalum,molybdenum or other highly refractory metal.

The dish-shaped contour of the header materially strengthens the headeragainst flexure and thus holds the cathode and control grid electrodesin place, and the length of the lead-in conductors is reduced withoutreducing the length of any of the insulating paths. My improved radiotube is easily made, the electrodes are accurately aligned and rigidlysupported, and the input electrodes are completely shielded from theoutput electrodes.

While only one embodiment of this invention is shown, it is to bedistinctly understood that the invention should not be limited preciselythereto.

What I claim is:

1. Radio frequency apparatus comprising a tube having a screen grid, ametallic screen grid support electrically connected to said screen grid,a metallic header member electrically connected to said screen gridsupport, a first condenser electrode electrically connected to saidheader member, a ground plate forming a second condenser electrode, anda sheet of insulation material interposed between said first and secondcondenser electrodes.

2. Radio frequency apparatus comprising a tube having a screen grid, ametallic screen grid support electrically connected to said screen grid.a metallic header member electrically connected to said screen gridsupport, a first condenser electrode electrically connected to saidheader member, a second condenser electrode, and a flat annular sheet ofmica insulation material interposed between said first and secondcondenser electrodes.

3. Radio frequency apparatus comprising a radio frequency tube having ascreen grid, 2.

- metallic screen grid support electrically connected to said screengrid, a metallic member electrically connected to said screen gridsupport, an annular metallic member forming a first condenser electrode,said annular metallic member I having a plurality of spring contactmembers which are positioned to be electrically connected to saidmetallic member, a ground plate forming a second condenser electrode,and an annular sheet of insulation material interposed between a saidfirst and second condenser electrodes.

CARROLL DALE KENTNER.

